The invention relates generally to wireless communication systems and more particularly to a communication method that uses time division duplexing.
In addition to traditional voice services, next generation wireless communication systems have to support various different types of multimedia services, including broadcasts, video conferencing, and interactive applications, for example. Many of these multimedia services may require flexibility in their use of spectrum capacity to operate effectively. The typical spectrum management approach is to assign frequencies to a particular use. This approach, however, has become somewhat limited in view of the complexity and overlap between the operations of next generation services and applications. One regulatory solution has been the introduction of flexible-use spectrum in which users of assigned portions of spectrum have more freedom to decide which technologies and services to deploy. In this regard, flexible-use spectrum can allow spectrum users to make timely commercial choices and can let market forces determine which competing technologies and services will be offered in a particular frequency band. Such approach can result in a more effective use of spectrum than that which occurs by imposing a technology or a service by regulation. As a result of these efforts to open up the spectrum, new user-based communication techniques are being considered that address aspects that are particular to next generation services and applications. For example, communication methods that include duplexing techniques or schemes that incorporate the inherent asymmetry in data flow that is characteristic of many multimedia services are being considered for next generation wireless communication systems.
Duplexing techniques include time division duplexing (TDD), frequency division duplexing (FDD), and/or hybrid duplexing, the latter of which includes aspects of both TDD and FDD schemes. In TDD, bidirectional communication or data flow is implemented through a communication link by separating the communication time within a given frequency band associated with the communication link into alternating transmission time slots and reception time slots. A time guard is used between time slots to reduce or minimize the likelihood of interference. In this scheme, a satellite or a base station, for example, can allocate a number of transmission time slots different from a number of reception time slots to a mobile device within a given time interval to produce asymmetric data communication. As the area of coverage provided by the satellite or the base station increases significantly, the guard time between time slots may be increased to compensate for delays that result from a longer signal round-trip between the satellite or base station and the mobile device. The increased delay can reduce the communication efficiency of the TDD scheme. In many instances, however, the time guard is sufficiently small even when large areas of coverage are concerned such that the TDD scheme efficiency remains adequate for many services or applications.
In FDD, bidirectional communication or data flow is implemented through a communication link by partitioning a given frequency band associated with the communication link into separate transmission and reception frequency bands that operate concurrently. Because the transmission and reception bands are separate from each other to reduce the likelihood of interference, no time delays occur associated with the transmission or reception of signals (i.e., no round-trip delays). Although the FDD scheme may be suitable for large areas of coverage because time delays do not play a significant role, the fixed and balanced nature of the transmission and reception frequency bands limit the flexibility that is necessary for asymmetric data communication in next generation wireless communication services. Some FDD schemes achieve asymmetry by using an auxiliary frequency band separate from the paired transmission and reception frequency bands to provide additional capacity in one direction of the data flow. This approach, however, requires the communication system to include additional hardware and/or software to handle the separate frequency band through which asymmetry is achieved.
Thus, a need exists for new methods for asymmetric communication in wireless communication systems.